The heart means love. A good heart means love to the Lord and to the neighbor, while a hard or stony heart means the love of self or the world -- riches and things. When the psalmist asks the Lord to search his heart, he wants the Lord to see what it is that he loves. And we are what we love. What we eat may form our earthly body, but it's only temporary, what we love forms our spiritual body, beautiful or ugly as we have chosen. It's interesting to note that the first multi-cellular motion of our embryo is the pulsating that starts in a twist of blood vessel that is to become our heart, and the last motion of our natural body is our heartbeat. It is there for all of our natural life. And of course there is a beating heart in our spiritual bodies when we come to put them on.

154. Internal Meaning of Ezekiel, Chapter 31

1-2 Of the natural man who is in knowledges [scientifica]. (11, 4)

3-9 In the Ancient Church a rational flourished that was derived from knowledges [scientifica] of every kind, through their confirming, by means of these, the Divine things of the church; and from this source they had spiritual intelligence. (11, 7)

10-13 The pride of self-intelligence, from which comes a trust in learning, has wholly cast them down from intelligence, and has deprived them of all the truths of the church. (3, 3)

14 They are cast into hell, that they may no longer destroy. (3, 15)

15-18 There they are shut up, lest, while continuing in their falsifications, they should spread their falsities abroad. (3, 15, 15)